Methods are currently known for grinding the unfinished edges of glass sheets as they are produced by cutting from the original production format to the actual use formats. In principle, grinding is applicable to any step of the machining of the glass sheet after cutting, for example before its use as is or as a necessary operation before tempering or as preparation of the glass sheet in order to obtain a uniform geometry and surface finish for particular uses, such as the composition of structural insulating glazing.
Grinding is performed for several reasons, which are listed here not in order of importance: the first reason relates to safety in handling the sheets, in which the edges would be dangerously sharp if they were not ground; the second one relates to the elimination of the edge defects of the sheets, typically so-called “microcracks”, which might trigger breakages of the sheet in the subsequent working steps (particularly tempering) and in the subsequent state of use; the third one can be simply the definition of the format of the glass sheet with better dimensions, geometry and surface finish than can have been achieved with the first working step, i.e., cutting, which leaves the edges unfinished, and this is done for architectural uses, for use in interior decoration, and in particular for use in the composition of structural insulating glazing; additional reasons may be the most disparate.
In order to better understand the configuration of the glass sheet, not so much in its possible isolated use, but most of all in its more widespread use in combination with other components to constitute the so-called “double glazing unit” or, more technically, “insulating glazing”, some concepts related to the intermediate component itself, i.e., the “glass sheet”, and the final product, i.e., the “double glazing unit”, are summarized hereinafter. The subsequent use of the double glazing unit, i.e., as a component of doors or windows or building faces, is known to the person skilled in the art and is not discussed here in detail.
With reference to FIG. 1A, the double glazing unit is constituted typically by two or more glass sheets 1001, 1002, which are mutually separated by one or more spacer frames 1003, which are hollow and have microperforations on the face directed toward the inside of the chamber.
The spacer frames 1003 usually contain, in their hollow part, hygroscopic material, which is not shown in the figure and is designed to absorb the moisture trapped during manufacture and/or any moisture that might subsequently penetrate due to seal defects. A chamber (or chambers) 1006 delimited by the glass sheets 1001 and 1002 and by the frame 1003 can contain air or gas or mixtures of gases injected therein, which provide the double glazing unit with particular properties, for example thermally insulating and/or soundproofing properties. The connection between the glass sheets and the frame is achieved by means of two levels of sealing: a first seal 1004 is designed to provide a hermetic closure and affects the lateral surfaces of the frame 1003 and the portions that are adjacent thereto of the glass sheets 1001, 1002; a second seal 1005 affects the compartment constituted by the outer surface of the frame and by the faces of the glass sheets up to the edge of such sheets and is designed to provide cohesion among the components and maintain the mechanical strength of the connection among them.
FIGS. 1A-1E show five possible sectional views of configurations of a double glazing unit, of which only the first one has been described above. However, it is straightforward to extend the comment provided above to the configurations shown in FIGS. 1B, 1C, 1D, 1E, related to examples of possible variations (double chamber, coated glass sheets, offset sheets, laminated sheets) and combinations of these variations. In the figure, the sun represents the outside environment of a building in which the double glazing units are installed, while the interior of the building is represented by a radiator.
The “glass sheets” used in the composition of the double glazing unit can have different shapes depending on their use; for example, the outer glass sheet 1001 (with respect to the building) can be normal or reflective (in order to limit heat input during summer months) or can also be laminated/armored (for intrusion/vandalism prevention functions) or can be laminated/tempered (for security functions) and can also be combined, for example reflective and laminated.
The inner glass sheet 1002 (with respect to the building) can be normal or of the low-emissivity type (in order to limit the dispersion of heat during winter months) or laminated/tempered (for security functions) or combined, for example low-emissivity and laminated.
In particular, FIGS. 1C, 1D, 1E illustrate an important category of insulating glazing, i.e., glazing also used with structural functions in addition to the particular functions of insulating glazing, i.e., the thermally and acoustically insulating functions. For this type of glazing, like the ones used in interior decoration, machining of the edge is necessary for correct definition of the dimensions, geometry and finish.
Currently it is known to perform this machining, which consists in grinding performed on the individual sheets, with a horizontal arrangement of the glass sheet on so-called two-sided machines or on so-called machining centers, or with a substantially vertical arrangement of the glass sheet on so-called beveling machines or on so-called arrissing machines.
In the first category, i.e., with a horizontal arrangement of the glass sheet, two-sided machines and machining centers, which are unexceptionable in terms of the results achieved in machining the edge of the glass sheet, machining centers in particular, by performing not only simple grinding but also contoured grinding in the perimeter and profiled grinding in the thickness (differently from beveling machines, which work only on rectangular glass sheets and provide only bevels in terms of profile), have the following problems: high costs and large space occupation.
In the second category, i.e., with a substantially vertical arrangement of the glass sheet, beveling machines, despite performing any profiled machining within the thickness of the edge, albeit only on straight sides, work only on one side at a time and are expensive, due to the large number of spindles, as well as slow in production; arrissing machines do not achieve the machining precision required for the uses cited earlier, since the reference of the machining of all four sides is always taken on the lower horizontal side, which is unfinished and irregular, i.e., as obtained by the cutting operation.
Further, with the exception of extremely expensive machining centers, all these machines can work only glass sheets of a rectangular format.
Respectively, Patent publications related to the background art cited above is as follows:
for the two-sided machine, EP1063053 B1, in the name of Z. Bavelloni S.p.A.;
for the machining center: EP0484674 B1, in the name of Intermac S.r.l.;
for beveling machines: EP0067469 B1, in the name of Elettromeccanica Luigi Bovone S.r.l.;
for arrissing machines: EP1769885 A1 in the name of this same Applicant.
None of these disclosures leads to the inventive advantages of the present application, which in summary consist in being able to perform, with a substantially vertical arrangement of the glass sheet, in a single machine and with an automatic feed, the working of the edge of the entire perimeter of the glass sheet, of any shape, without resting its lower edge on the conveyor.
EP1063053 B1, in addition to working on a sheet with a horizontal arrangement, in fact uses two machines and works only on rectangular sheets; EP0484674 B1, in addition to working on a sheet with a horizontal arrangement, requires complex manual positioning of the sheet; EP0067469 B1 performs work on a single rectilinear side of the sheet at a time; EP1769885 A1 keeps the glass sheet always rested on the conveyor.